U.S. patent number 10,428,184 [Application Number 15/302,335] was granted by the patent office on 2019-10-01 for method for producing a superhydrophobic membrane or surface coating of a substrate.
This patent grant is currently assigned to Universitaet Bayreuth. The grantee listed for this patent is UNIVERSITAT BAYREUTH. Invention is credited to Seema Agarwal, Mitsunobu Doimoto, Andreas Greiner.
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United States Patent |
10,428,184 |
Greiner , et al. |
October 1, 2019 |
Method for producing a superhydrophobic membrane or surface coating
of a substrate
Abstract
The invention concerns a method for producing a superhydrophobic
membrane or surface coating of a substrate from an aqueous phase
comprising the following steps: a) Preparing an aqueous dispersion
by dispersing particles of hydrophobic polymer(s) in an aqueous
solution of protic polymer(s), wherein the protic polymer(s) and
the hydrophobic polymer(s) are present in a weight ratio of protic
polymer(s):hydrophobic polymer(s) in a range of 5:95 to 22:78, b)
electrospinning the dispersion of step a) onto a carrier for
producing the membrane or onto the surface for producing the
surface coating thereby producing at least one fiber and a nonwoven
fabric from the fiber, c) subjecting the nonwoven fabric to a
sol-gel process, wherein a precursor/precursors of the sol-gel
comprise(s) an alkoxysilane, and d) curing the nonwoven fabric
obtained by step c) at a temperature in a range of 50.degree. C. to
150.degree. C.
Inventors: |
Greiner; Andreas (Bayreuth,
DE), Agarwal; Seema (Marburg, DE), Doimoto;
Mitsunobu (Mie, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
UNIVERSITAT BAYREUTH |
Bayreuth |
N/A |
DE |
|
|
Assignee: |
Universitaet Bayreuth
(Bayreuth, DE)
|
Family
ID: |
50486788 |
Appl.
No.: |
15/302,335 |
Filed: |
April 9, 2015 |
PCT
Filed: |
April 09, 2015 |
PCT No.: |
PCT/EP2015/057714 |
371(c)(1),(2),(4) Date: |
October 06, 2016 |
PCT
Pub. No.: |
WO2015/155285 |
PCT
Pub. Date: |
October 15, 2015 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20170022330 A1 |
Jan 26, 2017 |
|
Foreign Application Priority Data
|
|
|
|
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Apr 10, 2014 [EP] |
|
|
14164271 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D
7/65 (20180101); D01D 5/003 (20130101); B01D
67/0009 (20130101); C08J 3/07 (20130101); B01D
69/02 (20130101); D01F 6/44 (20130101); D06M
13/507 (20130101); D01F 1/10 (20130101); D06M
13/513 (20130101); B01D 67/0004 (20130101); D01F
6/50 (20130101); C09D 133/16 (20130101); B01D
2323/08 (20130101); B01D 2325/38 (20130101); C08J
2333/16 (20130101); B01D 2323/39 (20130101); C08J
2429/04 (20130101) |
Current International
Class: |
D01D
5/00 (20060101); B01D 67/00 (20060101); D01F
6/50 (20060101); D01F 1/10 (20060101); D06M
13/513 (20060101); C08J 3/07 (20060101); D06M
13/507 (20060101); C09D 7/65 (20180101); D01F
6/44 (20060101); B01D 69/02 (20060101); C09D
133/16 (20060101) |
Field of
Search: |
;464/484 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
102358067 |
|
Feb 2012 |
|
CN |
|
2267064 |
|
Feb 2006 |
|
EP |
|
2013/092862 |
|
Jun 2013 |
|
WO |
|
Other References
International Search Report dated Jul. 8, 2015 in PCT/EP2015/057714
(5 pages). cited by applicant .
Written Opinion dated Jul. 8, 2015 in PCT/EP2015/057714 (6 pages).
cited by applicant .
Agarwal et al., "Electrospinning of Fluorinated Polymers: Formation
of Superhydrophobic Surfaces", Macromol. Mater. Eng., 2006, 291,
592-601. cited by applicant .
Database WPI Week 201240 Thomson Scientific, London, GB; AN
2012-C94247 XP002730990, -& CN 102 358 067 A (UNIV JIANGNAN)
Feb. 22, 2012 (Feb 22, 2012) abstract. cited by applicant .
Gao et al., "Formation of Highly Hydrophobic Surfaces on Cotton and
Polyester Fabrics Using Silica Sol Nanoparticles and Nonfluorinated
Alkylsilane", Ind. Eng. Chem. Res., 2009, 48(22):9797-9803. cited
by applicant .
Li et al., "Superhydrophobic surfaces prepared from water glass and
non-fluorinated alkylsilane on cotton substrates", Applied Surface
Science, 2008, 254(7):2131-2135. cited by applicant .
Meng et al., "In-situ growth of titania nanoparticles in
electrospun polymer nanofibers at low temperature", Materials
Letters, 2009, 63(16):1401-1403. cited by applicant .
Satoh et al., "Preparation of Super-Water-Repellent Fluorinated
Inorganic-Organic Coating Films on Nylon 66 by the Sol-Gel Method
Using Microphase Separation", Journal of Sol-Gel Science and
Technology, 2003, 27(3):327-332. cited by applicant .
Stoiljkovic et al., "Preparation of water-stable submicron fibers
from aqueous latex dispersion of water-insoluble polymers by
electrospinning", Polymer, 2007, 48(14):3974-3981. cited by
applicant .
Wang et al., "Engineering biomimetic superhydrophobic surf aces of
electrospun nanomaterials", Nano Today (2011) 6, 510-530. cited by
applicant .
Xu et al., "Superhydrophobic cotton fabrics prepared by one-step
water-based sol-gel coating", The Journal of the Textile Institute,
vol. 103, No. 3, Mar. 2012, 311-319. cited by applicant.
|
Primary Examiner: Weddle; Alexander M
Attorney, Agent or Firm: Prismatic Law Group, PLLC
Claims
The invention claimed is:
1. Method for producing a superhydrophobic membrane or surface
coating of a substrate from an aqueous phase comprising the
following steps: a) Preparing an aqueous dispersion by dispersing
particles of hydrophobic polymer(s) in an aqueous solution of
protic polymer(s), wherein the protic polymer(s) and the
hydrophobic polymer(s) are present in a weight ratio of protic
polymer(s):hydrophobic polymer(s) in a range of 5:95 to 22:78, b)
electrospinning the dispersion of step a) onto a carrier for
producing the membrane or onto the surface for producing the
surface coating thereby producing at least one fiber and a nonwoven
fabric from the fiber, c) subjecting the nonwoven fabric to a
sol-gel process, wherein a precursor/precursors of the sol-gel
comprise(s) an alkoxysilane, and d) curing the nonwoven fabric
obtained by step c) at a temperature in a range of 50.degree. C. to
150.degree. C.
2. Method according to claim 1, wherein the particles of
hydrophobic polymer(s) comprise particles of a polyalkoxysiloxane
or of at least one of a polyacrylate, polymethacrylate, polyvinyl
ether or polystyrene or a mixture of these particles, wherein each
of the polyacrylate, polymethacrylate, polyvinyl ether and the
polystyrene comprises an at least partly fluorinated alkyl group or
aryl group.
3. Method according to claim 2, wherein the polyalkoxysiloxane
comprises linear and/or branched alkyl groups.
4. Method according to claim 3, wherein the alkyl groups are at
least partly fluorinated.
5. Method according to claim 1, wherein the particles have a grain
size in the range of 60 nm to 250 nm.
6. Method according to claim 1, wherein the protic polymer(s)
comprise(s) at least one of a polyvinyl alcohol (PVA), polyacrylic
acid, polymethacrylic acid, chitosan, agarose, polysaccharide,
polyethylenimine, methyl cellulose, polyester,
polyurea-formaldehyde, polymelamine-formaldehyde, carboxymethyl
cellulose, cyclodextrin, polyvinylpyrrolidone, gum arabic,
alginate, starch, gelatine, casein, poly glycidyl methacrylate, and
polyanhydride.
7. Method according to claim 1, wherein the protic polymer is PVA
and/or the hydrophobic polymer is poly (1H,1H,2H,2H-perfluorodecyl
acrylate).
8. Method according to claim 7, wherein the protic polymer(s) and
the hydrophobic polymer(s) are present in a weight ratio of protic
polymer(s):hydrophobic polymer(s) in a range of 8:92 to 20:80.
9. Method according to claim 8, wherein the protic polymer(s) and
the hydrophobic polymer(s) are present in a weight ratio of protic
polymer(s):hydrophobic polymer(s) in a range of 9:91 to 14:86.
10. Method according to claim 1, wherein an alkyl group/alkyl
groups of the alkoxysilane is/are at least partly fluorinated.
11. Method according to claim 1, wherein the alkoxysilane comprises
at least one methoxy group and/or at least one linear or branched
alkyl group comprising 5 to 30 carbon atoms.
12. Method according to claim 1, wherein the precursor(s)
comprise(s) tetraethylorthosilicate (TEOS).
13. Method according to claim 12, wherein the precursor(s)
comprise(s) tetraethylorthosilicate (TEOS) in an alcoholic acidic
solution.
14. Method according to claim 1, wherein the precursor(s)
comprise(s) n-decyl trimethoxysilane (DTMS).
15. Method according to claim 14, wherein the precursor(s)
comprise(s) n-decyl trimethoxysilane (DTMS) in an alcoholic acidic
solution.
16. Method according to claim 14, wherein TEOS and DTMS are present
as precursors in a molar ratio of TEOS:DTMS in a range of 0.3:0.06
to 1.0:0.5.
17. Dispersion comprising particles of hydrophobic polymer(s) in an
aqueous solution of protic polymer(s), wherein the protic
polymer(s) and the hydrophobic polymer(s) are present in a weight
ratio of protic polymer(s):hydrophobic polymer(s) in a range of
5:95 to 22:78, wherein the particles of hydrophobic polymer(s)
comprise particles of a polyalkoxysiloxane or of at least one of a
polyacrylate, polymethacrylate, or polyvinyl ether or a mixture of
these particles, wherein each of the polyacrylate,
polymethacrylate, and polyvinyl ether comprises an at least partly
fluorinated alkyl group or aryl group.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present invention is filed under 35 U.S.C. .sctn. 371 as the
U.S. national phase of International Application No.
PCT/EP2015/057714, filed Apr. 9, 2015, which designated the U.S.
and claims the benefit of European Patent Application No.
14164271.0, filed Apr. 10, 2014, each of which is hereby
incorporated in its entirety including all tables, figures, and
claims.
The invention concerns a method for producing a superhydrophobic
membrane or surface coating of a substrate, a use of a mixture of
substances for the production of a superhydrophobic membrane or
surface coating of a substrate, and a mixture of substances. A
surface is superhydrophobic if the contact angle of a water droplet
on this surface exceeds 150.degree. and in particular 160.degree..
Besides the contact angle hydrophobicity can be further defined by
a water-roll angle. For the determination of the water-roll angle a
plate is moveably joint to another plate. The sample to be examined
is placed on the moveably joint plate. After placing a drop of
water on the sample the moveably joint plate supporting the sample
is tilted to increasingly steep angles. The angle at which the drop
of water rolls down the surface is the water-roll angle. The
water-roll angle of a superhydrophobic surface is smaller than
20.degree. and in particular smaller than 10.degree.. A combination
of a high contact angle against water and a small water-roll angle
on a given membrane or substrate indicates its technical usability
as superhydrophobic membrane or substrate.
Known from EP 2 267 064 B1 is a process for preparing a hydrophobic
fluorinated polymer surface by use of a homopolymer. In this
process a solution of the homopolymer in a solvent selected from
the group consisting of tetrahydrofuran, dimethylformamide,
trichloromethane and combinations thereof, and preferably in a
mixture of tetrahydrofuran and dimethylformamide, is
electrospun.
Known from Agarwal, S. et al., Macromol. Mater. Eng. 2006, 291,
pages 592-601 is that superhydrophobic surfaces can be formed by
electrospinning of copolymers of polystyrene and pentafluorostyrene
dissolved in a mixture of the aprotic solvents tetrahydrofuran
(THF) and dimethylformamide (DMF). If the copolymers were dissolved
in a concentration of 5 and 2 wt.-% particles of 2-3 mm diameter
connected by nanofibers were generated. These nanofibers showed a
superhydrophobic effect. Fibers generated from the copolymer in a
higher concentration had a regular structure and showed a water
contact angle of 160.degree. whereas it was not possible to measure
the contact angle for the irregular structure because it was not
possible to keep a water droplet on it. Therefore, it is assumed
that the water contact angle is much more than 160.degree.. It is
concluded that electrospinning of fluorinated polymers under
suitable conditions to form micro particles interconnected with
nanofibers could provide a simple, one-step method for the
formation of superhydrophobic surfaces.
Wang, X. et al., Nano Today 2011, 6, pages 510-530 reviews the
engineering of biomimetic superhydrophobic surfaces of electrospun
nanomaterials. In this article it is concluded that fabricating a
surface with superhydrophobicity or superhydrophilicity requires a
rough surface structure. However, the surfaces show worse
mechanical stability with increasing roughness, which is the main
barrier preventing biomimetic superhydrophobic surfaces from
application in industry. Known superhydrophobic fibers produced by
electrospinning show no interfiber cohesion and no adhesion to
substrate surfaces. This results in a bad mechanical stability and
a bad abrasion resistance of surface coatings produced from these
fibers.
Known from Stoiljkovic A. et al., Polymer 48, 2007, pages 3974-3981
is the preparation of water-stable submicron fibers from aqueous
polystyrene latex dispersion of water-insoluble polymers by
electrospinning. The dispersion for electrospinning was prepared by
mixing of certain amounts of a latex dispersion and polyvinyl
alcohol (PVA) in water. The template polymer PVA was removed from
electrospun fibers after electrospinning by water extraction. After
the removal of the template polymer, the particles hold together
due to the attractive van der Waals' forces, which are acting
between the particles in the fibers. This results in specific
surface structures of the fibers.
The problem to be solved by the present invention is to provide a
novel method for producing a novel superhydrophobic material, a use
of a mixture of substances for producing this superhydrophobic
material and a mixture of substances.
The problem is solved by the features of claims 1, 14 and 15.
Embodiments of the invention are disclosed in claims 2 to 13.
According to the invention a method for producing a
superhydrophobic membrane or surface coating of a substrate from an
aqueous phase is provided. The method comprises the following
steps:
a) Preparing an aqueous dispersion by dispersing particles of
hydrophobic polymer(s) in an aqueous solution of protic polymer(s),
wherein the protic polymer(s) and the hydrophobic polymer(s) are
present in a weight ratio of protic polymer(s):hydrophobic
polymer(s) in a range of 5:95 to 22:78, b) electrospinning the
dispersion of step a) onto a carrier for producing the membrane or
onto the surface for producing the surface coating thereby
producing at least one fiber and a nonwoven fabric from the fiber,
c) subjecting the nonwoven fabric to a sol-gel process, wherein a
precursor/precursors of the sol-gel comprise(s) an alkoxysilane,
and d) curing the nonwoven fabric obtained by step c) at a
temperature in a range of 50.degree. C. to 150.degree. C.
The substrate may be a glass, a metal, a plastic, a textile or a
nonwoven, such as a fleece. During the sol-gel process the
precursor or the precursors of the sol-gel transform(s) into a
colloidal solution (sol) and then into an integrated network (gel).
The transformation may occur by hydrolysis upon contact of the
precursor(s) with water. Subjecting the nonwoven fabric to the
sol-gel process in step c) usually occurs by contacting the
nonwoven fabric with the precursor or precursors of the sol-gel
during the reaction of the precursor(s) into the sol and the gel.
The contacting may be performed by dipping or by coating. The
sol-gel process is usually started by contacting or mixing the
alkoxysilane with water.
The inventors recognized that known superhydrophobic fibers having
a structure of particles connected by fibers, i.e. a structure like
a string of pearls, as well as nonwovens consisting of these fibers
adhere bad on substrates and are characterized by a bad cohesion of
the fibers. Therefore, a practical application of this kind of
fibers seems to be difficult.
Surprisingly, it has been found that a nonwoven fabric produced
according to the method of the invention is superhydrophobic though
the fibers have no structure like a string of pearls. Scanning
electron microscope (SEM) micrographs showed that the fibers have a
cylindrical form and a porous surface. Furthermore, it has been
shown that solely coating the fibers resulting from step b) with
alkoxysilanes does not result in a superhydrophobic character of
the fibers. The sol-gel process is essential for providing
superhydrophobicity. It has been found that the nonwoven fabric
produced according to the method of the invention adheres well to
substrates. Furthermore, the fibers of the nonwoven fabric produced
according to the method of the invention showed cohesion resulting
in a high mechanical stability of the fabric. A further feature of
the nonwoven fabric produced according to the method of the
invention is that the particles are encapsulated and--if the
hydrophobic polymer(s) forming the particles are at least partly
fluorinated--that no contamination of the surroundings with
fluorinated polymer(s) occurs. A particular interesting feature of
the membrane or surface coating produced according to the method of
the invention is that the membrane or surface coating are
self-cleaning upon contact with liquid water.
In the electrospinning processes known from EP 2 267 064 B1 and
from Agarwal, S. et al., Macromol. Mater. Eng. 2006, 291, pages
592-601 organic solvents are used. These solvents make the
procedures costly because specific materials have to be used for
handling the solvents, measures have to be taken to prevent the
solvents from taking fire or exploding and after use environmental
protection aspects have to be considered.
A main advantage of the method according to the invention is that
the dispersion is produced according to step a) by dispersing
particles in an aqueous solution of protic polymer(s). By use of
water as solvent the disadvantageous accompanying organic solvents
are avoided. This makes the production of the superhydrophobic
membrane or surface coating of a substrate much cheaper than a
production using an organic solvent for the electrospinning
process.
The particles of hydrophobic polymer(s) may comprise particles of a
polyalkoxysiloxane or of at least one of a polyacrylate,
polymethacrylate, polyvinyl ether or polystyrene or a mixture of
these particles, wherein each of the polyacrylate,
polymethacrylate, polyvinyl ether and the polystyrene comprises an
at least partly fluorinated alkyl group or aryl group. The
fluorinated alkyl group or aryl group may be perfluorinated. The
polymer(s) may be homo- or copolymer(s) or blends of the polymers.
It is also possible that a mixture of particles of different
polymers is used in step a). The particles may have a grain size in
the range of 60 nm to 250 nm.
The polyalkoxysiloxane may comprise linear and/or branched alkyl
groups. In one embodiment the alkyl groups are at least partly
fluorinated.
In one embodiment the protic polymer(s) comprise(s) at least one of
a polyvinyl alcohol (PVA) polyacrylic acid, polymethacrylic acid,
chitosan, agarose, polysaccharide, polyethylenimine, methyl
cellulose, polyester, polyurea-formaldehyde,
polymelamine-formaldehyde, carboxymethyl cellulose, cyclodextrin,
polyvinylpyrrolidone, gum arabic, alginate, starch, gelatine,
casein, poly glycidyl methacrylate, and polyanhydride. The protic
polymer(s) may be homopolymer(s) or copolymer(s).
The protic polymer may be PVA and/or the hydrophobic polymer may be
poly((1H, 1H, 2H, 2H) perfluorodecyl acrylate) (=FD). The protic
polymer(s) and the hydrophobic polymer(s) may be present in a
weight ratio of protic polymer(s):hydrophobic polymer(s) in a range
of 8:92 to 20:80, in particular 9:91 to 14:86. If it is in the
range of 5:95 to 14:86 it has been found that the surface is not
only superhydrophobic but also oliphobic. Depending on the weight
ratio of protic polymer(s):hydrophobic polymer(s) surfaces with
different functionalities can be obtained.
An alkyl group/alkyl groups of the alkoxysilane may be at least
partly fluorinated. The alkoxysilane may comprise at least one
methoxy group and/or at least one linear or branched alkyl group
comprising 5 to 30 carbon atoms.
In one embodiment the precursor(s) comprise(s)
tetraethylorthosilicate (TEOS). Alternatively or in addition the
precursor(s) may comprise n-decyl trimethoxysilane (DTMS). The TEOS
and/or the DTMS may be present in an alcoholic acidic solution.
TEOS and DTMS may be present as precursors in a molar ratio of
TEOS:DTMS in a range of 0.3:0.06 to 1.0:0.5. For example, the molar
ratio of TEOS:DTMS:ethanol:HCl may be 0.5:0.1:28.9:0.008.
The substrate may comprise a textile or a nonwoven, such as a
fleece, a filter, a glass, a plastic, a ceramic, a paper, or a
metal. Each of the textile and the nonwoven may comprise natural
and/or artificial fibers. The substrate may be an object of
utility.
In one embodiment of the method according to the invention the
nonwoven fabric is cured at a temperature in the range of
70.degree. C. to 90.degree. C. The curing may be performed for a
period in a range of 1 minutes to 60 minutes, preferably 5 minutes
to 15 minutes.
It has been recognized that relative humidity during
electrospinning influences the geometry of the resulting fiber.
Relative humidity during step b) may be lower than 30%, in
particular lower than 20%.
The invention further concerns the use of a dispersion comprising
particles of hydrophobic polymer(s) in an aqueous solution of
protic polymer(s), wherein the protic polymer(s) and the
hydrophobic polymer(s) are present in a weight ratio of protic
polymer(s):hydrophobic polymer(s) in a range of 5:95 to 22:78 for
the production of a superhydrophobic membrane or surface coating of
a substrate. The superhydrophobic surface coating of a substrate
can be used to provide the surface of the substrate with a
self-cleaning ability. Such a feature is particularly useful for
surfaces that are usually located outdoor and thereby become
polluted by particles such as soot particles. Such a surface can
then be cleaned by raindrops running down the surface which
raindrops collect the particles from the surface.
The particles of the hydrophobic polymer(s) may comprise particles
of a polyalkoxysiloxane or of at least one of a polyacrylate,
polymethacrylate, polyvinyl ether or polystyrene or a mixture of
these particles, wherein each of the polyacrylate,
polymethacrylate, polyvinyl ether and the polystyrene comprises an
at least partly fluorinated alkyl group or aryl group. The
polyalkoxysiloxane may comprise linear and/or branched alkyl
groups. The alkyl groups may be at least partly fluorinated. The
particles may have a grain size in the range of 60 nm to 250 nm.
The protic polymer(s) may comprise at least one of a polyvinyl
alcohol (PVA), polyacrylic acid, polymethacrylic acid, chitosan,
agarose, polysaccharide, polyethylenimine, methyl cellulose,
polyester, polyurea-formaldehyde, polymelamine-formaldehyde,
carboxymethyl cellulose, cyclodextrin, polyvinylpyrrolidone, gum
arabic, alginate, starch, gelatine, casein, poly glycidyl
methacrylate, and polyanhydride. The protic polymer may be PVA
and/or the hydrophobic polymer may be poly((1H, 1H, 2H, 2H)
perfluorodecyl acrylate) (=FD). The protic polymer(s) and the
hydrophobic polymer(s) may be present in a weight ratio of protic
polymer(s):hydrophobic polymer(s) in a range of 8:92 to 20:80, in
particular 9:91 to 14:86.
The invention further concerns a dispersion comprising particles of
hydrophobic polymer(s) in an aqueous solution of protic polymer(s),
wherein the protic polymer(s) and the hydrophobic polymer(s) are
present in a weight ratio of protic polymer(s):hydrophobic
polymer(s) in a range of 5:95 to 22:78, wherein the particles of
hydrophobic polymer(s) comprise particles of a polyalkoxysiloxane
or of at least one of a polyacrylate, polymethacrylate, or
polyvinyl ether or a mixture of these particles, wherein each of
the polyacrylate, polymethacrylate, and polyvinyl ether comprises
an at least partly fluorinated alkyl group or aryl group. The at
least partly fluorinated alkyl group or aryl group may be
perfluorinated.
EMBODIMENTS OF THE INVENTION
FIGS. 1a and 1b SEM micrographs of electrospun PVA (17%)-FD (83%)
composite fibers at different magnifications.
FIG. 2 shows a table comparing the features of different nonwovens
produced from different compositions of PVA-FD by the method
according to the invention comprising a sol-gel process with TEOS
and DTMS and before the sol-gel process.
15 wt.-% PVA aqueous solution was mixed with an aqueous dispersion
of poly((1H, 1H, 2H, 2H) perfluorodecyl acrylate) (=FD), average
particle grain size=110 nm (measured by dynamic light scattering)
at several solid ratios. Electrospinning with a standard one-needle
set-up was carried out at 23.degree. C. and 14% relative humidity.
The solutions were filled in a 2.5 ml syringe attached with a blunt
steel needle of 1.2 mm inner diameter. A rotating round steel plate
(diameter=15 cm) as counter electrode was placed 11 cm away from
the needle tip. The positive power supply was attached to the
needle and the negative power supply was attached to the counter
electrode. The voltage was applied at 30 kV, and electrospun fiber
mats were deposited on aluminum, cotton, glass or paper attached on
steel plate.
The nonwoven fabrics were subjected to the sol-gel process to
modify surface property. For this purpose a sol-gel solution with a
molar ratio of orthosilicate (TEOS):n-decyl trimethoxysilane
(DTMS):ethanol:HCl being 0.5:0.1:28.9:0.008 was prepared along with
strong stirring at room temperature for 30 min. The nonwoven
fabrics were immersed into the sol-gel solution for 5 seconds and
then cured in an oven for 10 min.
The electrospun fibers showed a cylindrical structure (FIG. 1a). At
higher magnification the dispersion particles embedded in the PVA
matrix can be identified (FIG. 1b).
The results obtained with different PVA-FD compositions are given
in FIG. 2. HP-53 is a preparation of FD having a grain size of
about 100 nm. HP-53 is dispersed in an aqueous solution of PVA in
ratios of PVA:FD of 10:90 (sample 1), 17.5:82.5 (sample 2), 27:73
(sample 3) and 50:50 (sample 4). It can be clearly seen that all
compositions show contact angles against water <50.degree.
before sol-gel treatment. However, after sol-gel treatment with
TEOS/DTMS the different compositions show significantly different
behavior. The sol-gel treated electrospun nonwovens prepared with a
composition of PVA:FD of 10:90 (sample 1) and 17.5:82.5 (sample 2)
showed superhydrophobic behavior. Sol-gel treated electrospun
nonwovens with compositions of PVA:FD of 27:73 (sample 3) and 50:50
(sample 4) showed no superhydrophobic behavior which is very
remarkable as with higher content of fluorinated compound lower
contact angles were found. In contrast, sol-gel treated pure PVA
fibers showed a contact angle of 89.degree. (sample 5). Indeed,
there is a window of compositions for PVA:FD which provides after
sol-gel treatment superhydrophobicity of the nonwovens. It is
obvious from the SEM micrographs, that the superhydrophobic fibers
show high porosity after sol-gel treatment (FIG. 2). Interestingly,
for sample 1 next to superhydrophobicity oleophobic behavior was
found whereas sample 2 showed also superhydrophobicity but not
oleophobic behavior. This means, that depending on the composition
of PVA:FD samples with different functionality can be obtained.
Sample 2 has double function in terms of water repellence and
water/oil separation whereas as sample 1 has double function in
terms of water and oil repellence. A tape test showed for samples 1
and 2 very good adhesions to glass and metal (Al) surfaces.
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